1. Field of the Invention
The invention relates to the technical field of food processing, and more particularly to a production method of a clear, concentrated sweet potato juice.
2. Description of the Related Art
At present, the sweet potato juice is mostly extracted by hot squeezing. The conventional hot squeezing type production process of a sweet potato juice is as follows: taking fresh sweet potatoes as the raw material; preparing a paste by peeling, crushing, and high-temperature gelatinization; squeezing and saccharifying to obtain a sweet potato paste; and filtering the sweet potato paste to obtain the sweet potato juice.
However, after the crushed sweet potatoes are gelatinized at high temperature, the celluloses of the paste are destroyed. A lot of pulp overflows during the squeezing process and is attached onto the press belt. Thus, the juice yield is reduced; the squeezed juice contains a lot of pulp, which increases cost and difficulty for the subsequent filtering and clarification.
Moreover, the overflow of the sweet potato paste will become more serious along with the rise of temperature and the extension of acting time of the sweet potato paste, thus the catalytic temperature and time of thermostable a-amylase during the decomposition of starch in the sweet potato paste are affected, which is unfavorable to the full conversion of starch in the paste.
The sweet potato skin and skin dregs (generally called sweet potato residue) are separated during the peeling and squeezing process of sweet potato in the prior art. The content of sweet potato residue is generally up to 40-55 wt. % in the prior art. The sweet potato residue contains a large number of dietary fibers which have important physiological function to human body.
The dietary fiber includes two basic types when it is dissolved in water:water soluble fiber and water insoluble fiber. The water soluble fiber can slow down the digestion rate and excrete cholesterol rapidly, so that the blood glucose and cholesterol can be controlled at an optimal level. The water insoluble fiber can reduce the risk of bowel cancer, prevent constipation and diverticulitis by absorbing the toxic substances in food, and reduce the toxins from bacteria in the digestive tract.
However, the sweet potato skin and sweet potato residue are usually used as fertilizer in the prior art, some are used as feed after treatment, and the active ingredients are not fully utilized.